Transistors, in particular MOS (Metal-Oxide-Semiconductor) transistors, such as MOSFETs (Metal-Oxide-Semiconductor Field-Effect Transistors) or IGBTs (Insulated Gate Bipolar Transistors) are widely used as electronic switches in a variety of different applications, such as drive applications, power conversion applications, automotive applications, consumer electronic applications, and the like. It is desirable for those transistors to have a predefined voltage blocking capability, which is dependent on the specific application, and to have a low on-resistance, which is the electrical resistance of the transistor in an on-state.
MOS transistors used as electronic switches (that are often referred to as power MOS transistors) include a drift region between a body region and drain region (also referred to as emitter region in an IGBT). The on-resistance and the voltage blocking capability of the transistor device is mostly defined by a length of this drift region between the body region and the drain region, and the doping concentration of this drift region. In general, the on-resistance decreases as the doping concentration increases and/or as the length decreases. However, an increased doping concentration and/or a decreased length may cause a decreased voltage blocking capability.
One way to increase the voltage blocking capability without increasing the on-resistance is to provide a field electrode adjacent the drift region, dielectrically insulated from the drift region, and coupled to a source terminal of the MOS transistor. Usually, a power transistor includes a plurality of transistor cells connected in parallel, with each of these transistor cells including a field electrode, and a drift region between two adjacent field electrodes.
There is a need to provide a transistor device that includes a field electrode, and that has a reduced size.